deal with missing values

[calvinmetcalf]

both of the ,, and NULL variety inspired by mafintosh/csv-parser#31

[max-mapper]

Hmm, while I can see the benefit of this in certain situations, it can be considered 'lossy' since an empty field and NULL could mean different things semantically. Kind of like how we added integer parsing support but then reverted it because I decided everything in CSV should be treated as a string #15 (comment)

Maybe by that logic then ,, should turn into "", and ,NULL, into "NULL"

[calvinmetcalf]

so normally I'd agree but on the other hand this is the default way sqlserver generates CSVs and somebody complaining about 'why is my text field full of NULL strings is how this came to my attention. I could just filter out all NULL values but since sqlserver does go to the trouble of quoting some things that means if we treat NULL and 'NULL' the same we may be loosing info.

[max-mapper]

Hmm yea that makes sense, you need the parser to do it. Maybe we can make this optional? E.g. an optional test here and an option in the parser

[calvinmetcalf]

sounds sensible